The present invention relates to improvements in methods and apparatus for performing cuts in subterranean wells and, more particularly, to methods and apparatus for using linear focused explosives to form endless cuts in the confines of a subterranean well.
From time to time it is necessary to perform machining functions at subsurface locations in subterranean wells. For example, if a window in a subterranean casing is desired to allow the drilling or formation of a branch bore, the typical process involves utilizing a whipstock with a milling or cutting tool to mill a window in the casing. If a downhole tool such as a whipstock, whipstock-packer assembly or the like blocks the bore of a subterranean well, typically an opening can be cut through the obstruction using a mill or drill. If an axial length of casing is to be removed to allow undercutting, an undercutting tool is lowered into the well to mill out the casing section and surrounding cement as desired.
The prior art methods and apparatus utilized to perform these subsurface operations are expensive because they are time consuming and involve sophisticated milling equipment.
The present invention contemplates improved methods and apparatuses for performing subsurface cutting operations in a subterranean well. The invention uses linear shaped charges and related methods to perform subsurface cutting and shaping. Linear shaped charges are devices which utilize focused explosive reactions to produce cuts along a line in hard materials. In other words, linear shaped charges are generally symmetrical about a line and make linear cuts.
The present invention utilizes linear shaped charges prearranged on an apparatus to form an endless pattern corresponding to the periphery of an opening to be formed. The linear shaped charges are lowered into the well to a location adjacent to the site of the proposed cut and discharged to cut through the wall of the tubing, casing, or other structure along the periphery of the opening to be formed. For example, when the casing is to be cut, an endless pattern of linear shaped charge is formed at the surface on an apparatus and carried downhole. When the charge is exploded, an endless cut around the opening in the casing is formed. The plug formed by the cut can be removed as a single piece or cut into smaller sections and removed or milled. In other applications downhole objects other than casing are cut, such as, whipstocks, packers, liners, and the like.
According to another aspect of the present invention, the apparatus can carry one or more patterns of linear charges so that cutting can be performed at two or more spaced points. Removal of the casing can be achieved conventionally or by sectioning the severed casing portions with linear shaped charge patterns extending between the two or more circumferential cuts. Thus, the present invention contemplates using linear shaped charges to sever or disconnect a section of casing and cut it into small pieces so that it can be removed from the well.
According to the present invention, a shaped window can be formed in the wall of tubing, such as the casing or liner of a subterranean well, by first arranging linear charges to form a pattern according to the desired shape, lowering the charges downhole on a carrier to a preselected location, and discharging the linear shaped charge pattern to cut the desired shaped plug or section from the wall of the well tubing. The cut plug can thereafter be removed by conventional fishing techniques or may be cut into smaller pieces by using linear shaped charges.
The present invention also contemplates the utilization of staged detonations of individual segments of the pattern to be cut. For example, the side or axially extending portions of a casing window could be cut in one or more steps and the circumferential, or top and bottom, portions of the window could be cut in separate steps with indexing of the charge carrier in the casing to insure intersection of the successive cuts. In this manner a plurality of linear shaped charges or segments could be arranged to form an endless pattern. The charges forming the segmented portions of the charge patterns could be separated on the carrier radially. In this case the carrier could be indexed in position and rotated between successive segment firings. The charges forming segments of the pattern could be axially spaced allowing the carrier to be progressively moved axially to perform the sequential detonations. The charge segments could be on one carrier or separate carriers. Similar methods and apparatus could be applied to cut other type of tubings, such as, liners and the like at a subsurface location.
According to another embodiment of the present invention, a whipstock or packer can be used to drill and complete a branch bore. For example, an opening can be formed in the whipstock by use of a linear shaped charge pattern either mounted in the whipstock itself or in a carrier subsequently placed adjacent to the whipstock. According to this embodiment, an opening is formed in the whipstock or packer by discharging a linear shaped charge arranged in an endless pattern to allow access through the whipstock or packer to the well located therebelow.
According to another aspect of the present invention, linear shaped charges can be used to form complicated shaped openings in the wall of a casing, including shapes such as bayonet slots, rectangles, and the like which cannot be formed by conventional milling techniques. The ability to form unique and complicated shaped windows in casings allows for locator and mechanical locking connections with the casing wall which have heretofore been impossible to form. These methods of forming special shaped openings can, of course, be used in other well structures besides casings.